Introductory video created by Dr James Loudon: here (external website).

This work is part of the EPSRC-funded Skyrmion Project (link - external website).

Magnetic skyrmions resemble magnetic vortices and arise because of the competing interactions that occur in certain magnetic materials. They were discovered in 2009 and this has prompted an intense research effort as they could be used as magnetic bits for a new type of computer memory, called a racetrack memory. Unlike a conventional hard-drive, a racetrack memory has no moving parts and bits are moved along a wire by an electrical current. Skyrmions are attractive for this application because they can be moved by currents a million times smaller than those required to move ferromagnetic domains.

Skyrmions can be imaged using transmission electron microscopy and appear as white circles when the magnetisation is rotating in one direction and black when it rotates in the other. Recently, images have been published showing magnetic objects that appear half white and half black like the one in the figure. These were identified as a new magnetic object called a biskyrmion which consists of a pair of counter-rotating magnetic vortices. We searched for biskyrmions using a combination of electron microscopy, x-ray holography and micromagnetic simulations. This showed that there is no evidence that the biskyrmion state exists. The images can be explained as conventional magnetic bubble domains and the counter-rotating vortices result from the magnetic flux density associated with this object, not the magnetisation.

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